Baby mice born proof that mouse can be created by stem cells

Baby mice born in Japan are proof that mouse stem cells taken from embryos or created by reprogramming fetal tissue can be used to make viable egg cells. Scientists in Japan report they have created eggs from stem cells in a mammal for the first time. And the researchers went on to breed healthy offspring from the eggs they created.

While the experiments involved mice, the work is being met with excitement — and questions — about doing the same thing for humans someday.

“Wow. That’s my general reaction,” said Hank Greely, a bioethicist at Stanford University who studies stem-cell science. “Repairing hearts, repairing brains, repairing kidneys, that’s all good and important, and we’d all love to be able to do that. But this involves making the next generation.”

Scientists obtain the versatile cells from embryos. Embryonic stem cells are controversial because researchers destroy the embryos to get them.

These are cells that look essentially identical to embryonic stem cells. But instead of coming from embryos, they can be made from adult cells, such as skin or blood cells. So they don’t have any of the ethical baggage of embryonic cells.

“They’re gotten to what was our Holy Grail, which is making eggs,” said George Daly, a leading stem-cell scientist at Harvard. “It’s like cellular alchemy. I mean they can turn lead into gold here. They can turn skin cells or blood cells into eggs.”

“If it is dependent on fetal ovaries, that makes it completely impractical for human use,” says Jonathan Tilly, a reproductive biologist at Massachusetts General Hospital and Harvard Medical School in Boston. The method also requires surgery to put the reconstituted ovary into a body to mature, and more surgery to retrieve the eggs — another possible barrier for use in people.